The accurate representation, storage and transmission of color video images entails the processing of enormous amounts of data. In order to provide good resolution, i.e., to establish proper distinction between closely spaced variations within the original image, the system must be capable of representing the original image with as many pixels as possible. Further, in order to distinguish between closely related hues of color within the image, the system must be able to identify a multitude of colors which in turn requires increased information to be stored for each pixel. Since the large amount of data involved in normal digital color processing directly contributes to increased expense due to unwieldy processing, enlarged storage needs and increased transmission costs, a variety of encoding systems are prevalent in the art.
Such systems are based on various data compression techniques which are aimed at relatively efficient coding of picture material and provide the opportunity for significantly decreasing transmission costs and storage requirements for a given picture quality. A major disadvantage of such conventional compression and coding techniques is that they entail complex computational schemes at the encoding end as well as the decoding end.
A variety of block coding techniques have also been suggested for information compression in the coding of still pictures. For example, Mitsuya et al. U.S. Pat. No. 4,238,768 discloses a method by which a frame of grey scaled pictures is divided into a plurality of blocks, with the picture elements of each block being separated into grey components and resolution components on the basis of the statistical property of the luminance levels of picture elements within the block before the actual coding begins. A similar technique is also disclosed in Mitsuya et al. U.S. Pat. No. 4,205,341 wherein the size of each block is changed in accordance with the property of the picture and the portion corresponding to the block. Various adaptations of such information compression coding techniques to color pictures are disclosed by Mitsuya et al. U.S. Pat. No. 4,319,267 which teaches the separation of the color picture into three discrete color component pictures, which are subsequently divided into blocks by three discrete block coding means and encoded. However, these methods generally involve complex color encoding algorithms, complicated and expensive decoding means, and do not provide conveniently controllable multiple levels of compression which permit the user a choice of encoding best suited to his application.
More advanced block encoding and decoding processes for color images, using color map memories, are described in Campbell et al. U.S. Pat. No. 4,580,134.